Gate valves are generally comprised of a valve body having a central axis aligned with inlet and outlet passages, and a space between the inlet and outlet passages in which a slide, or gate, is moved perpendicular to the central axis to open and close the valve. In the closed position, the gate surfaces typically seal against sealing rings, which surround the fluid passage through the valve body. Gate valves, along with other valve types such as orbit, and butterfly valves, are used to control the flow of a great variety of fluids. Often the fluid to be controlled by the gate valve is under pressure. In the petroleum industry, gate valves are used along piping at various locations, and in particular are used in piping referred to in the petroleum industry as a Christmas tree, which is used as part of a drilling operation.
Actuators to open and close the gate valves include manual operators, diaphragm-type operators, and piston-type operators. Actuators often include a bonnet assembly, which interconnects the valve body and the valve gate, and a bonnet stem, which is movable with the gate via an operator stem.
In many applications in the petroleum industry, actuators have a top shaft extending from the distal end of the actuator such that a worker is able to determine whether the valve is in an open position or a closed position. However, in other applications, such as in a Christmas tree application, the positioning of gate valves is somewhat restricted. In such cases, actuators used to open and close the valves generally do not include a top stem indicator. Similarly, as may be the in manual operation with a turn wheel, a top stem indicator is generally not available due to the positioning of the turn wheel on the actuator.